A method for resourceful treatment of high-salinity wastewater

Abstract

The application provides a resource treatment method of high-salt wastewater, and the method comprises the following steps: (1) mixing the high-salt wastewater with a precipitant, stirring and reacting, and then performing solid-liquid separation to obtain a first filtrate; (2) performing freezing crystallization on the first filtrate, and then performing solid-liquid separation to obtain sodium sulfate and a second filtrate; (3) performing multi-effect evaporation on the second filtrate, and then performing solid-liquid separation to obtain sodium chloride and a third filtrate; (4) performing cooling crystallization on the third filtrate, and then performing solid-liquid separation to obtain potassium chloride and a fourth filtrate; and the fourth filtrate is recycled to the freezing crystallization in step (2). Through the freezing crystallization, multi-effect evaporation, cooling crystallization and recycling in sequence, the sodium and potassium in the high-salt wastewater can be effectively separated and recovered, the sodium sulfate, sodium chloride and potassium chloride products with industrial value can be produced, the salt content in the wastewater is reduced, and the resource utilization of the wastewater is realized.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment technology, specifically relating to a resource-based treatment method for high-salinity wastewater. Background Technology

[0002] With the rapid development of industry, the amount of high-salinity wastewater generated is increasing day by day, and its treatment has become a major challenge in the field of environmental protection. High-salinity wastewater mainly comes from industries such as chemical, pharmaceutical, petroleum, papermaking, dairy processing, and food canning. This wastewater contains a large amount of dissolved inorganic salts, such as sodium chloride and sodium sulfate, and may also contain a certain proportion of organic matter.

[0003] Currently, high-salinity wastewater treatment technologies suffer from problems such as resource waste, incomplete treatment, and environmental pollution. In particular, it is difficult to balance economic efficiency and environmental protection requirements in the effective recovery of sodium and potassium salts from high-salinity and high-sulfur wastewater. Traditional treatment methods include: (1) Direct evaporation concentration method: This method concentrates sodium and potassium salts by heating and evaporating water in wastewater. However, it has extremely high energy consumption and economic costs. In addition, due to the scaling problem caused by high concentration of salts during evaporation, equipment maintenance is frequent, reducing the feasibility and stability of the process. (2) Chemical precipitation method: By adding chemical agents to wastewater, heavy metal ions in the wastewater are precipitated into insoluble precipitates, reducing the heavy metal content. However, this method is not suitable for the precipitation of sodium and potassium salts. (3) Membrane separation: Membrane separation technology (such as reverse osmosis, nanofiltration, electrodialysis, forward osmosis, etc.) is often used for the preliminary treatment of high-salt wastewater. The advantage of this method is that the energy consumption is relatively low. However, under high salt concentration conditions, the membrane is easily fouled and clogged, requiring frequent replacement and cleaning, which leads to increased operating costs. In addition, the membrane separation method is difficult to achieve for the precise separation of sodium and potassium salts, resulting in low product purity. (4) Multi-effect evaporation combined with crystallization: In existing technologies, the process of combining multi-effect evaporation and crystallization is used for the resource-based treatment of wastewater. By separating different salts through stepwise evaporation and crystallization, the energy consumption of this method is lower than that of single-effect evaporation. However, it still faces problems such as high energy consumption, complex equipment, and high operation and maintenance costs.

[0004] Although the above treatment methods can achieve wastewater treatment to a certain extent, there are a series of problems in practical applications, such as: (1) High energy consumption: Traditional evaporation concentration and multi-effect evaporation processes require a lot of heat energy, especially for the treatment of high salt concentration solutions, resulting in high overall process operating costs; (2) Low product purity: Chemical precipitation and membrane separation methods cannot guarantee the high purity of the final product. Often, due to impurities or differences in membrane selectivity, the purity of sodium and potassium salts is not high, which limits their industrial application value; (3) Frequent equipment maintenance: Scaling and clogging problems exist in the evaporation and membrane separation process, requiring frequent cleaning and maintenance of equipment. This not only increases the operating cost of the equipment but also affects the continuity and stability of the process; (4) Environmental pollution: Chemical precipitation will generate a large amount of solid waste. If not treated properly, it will cause secondary pollution to the environment. Direct discharge of high-salt wastewater after evaporation concentration will also cause serious harm to the surrounding environment.

[0005] In conclusion, developing an efficient, economical, and environmentally friendly high-salinity wastewater treatment technology has significant practical implications and broad application prospects. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a resource-based treatment method for high-salinity wastewater. This invention, through sequential processes of freeze crystallization, multi-effect evaporation, cooling crystallization, and recycling, effectively separates and recovers sodium, potassium, and other components from high-salinity wastewater, producing industrially valuable sodium sulfate, sodium chloride, and potassium chloride products. This reduces the salt content of the wastewater and achieves resource utilization of the wastewater.

[0007] To achieve this objective, the present invention employs the following technical solution:

[0008] This invention provides a method for the resource-based treatment of high-salinity wastewater, the method comprising the following steps:

[0009] (1) Mix high-salt wastewater and precipitant, stir and react, then perform solid-liquid separation to obtain primary filtrate;

[0010] (2) The primary filtrate obtained in step (1) is subjected to freeze crystallization, and sodium sulfate and secondary filtrate are obtained after solid-liquid separation;

[0011] (3) The secondary filtrate obtained in step (2) is subjected to multi-effect evaporation, and after solid-liquid separation, sodium chloride and tertiary filtrate are obtained;

[0012] (4) Cool the filtrate obtained in step (3) to crystallize it, and after solid-liquid separation, potassium chloride and filtrate were obtained.

[0013] The four filtrates are reused for the freeze crystallization in step (2).

[0014] In this invention, a combination of freezing crystallization, evaporation crystallization and cooling crystallization is used to achieve the stepwise recovery of sodium sulfate, sodium chloride and potassium chloride, and the recovery rates of sodium sulfate, sodium chloride and potassium chloride are not less than 90%, which meets the usage standards of the chemical, agricultural and food industries.

[0015] In addition, the multi-effect evaporation technology used in this invention can significantly reduce energy consumption, and can reduce steam consumption by about 30 to 50 degrees compared with traditional single-effect evaporation.

[0016] Furthermore, the resource-based treatment method provided by this invention removes heavy metals from wastewater using a precipitant with a removal rate of no less than 95%, effectively reducing the impact of heavy metals on subsequent crystallization processes. In addition, by recycling the filtrate four times, zero discharge of wastewater is achieved during the treatment process, significantly reducing the pollution load on the environment.

[0017] The high-salt wastewater described in this invention comes from the solution of zinc oxide collected in a rotary kiln after alkali washing.

[0018] As a preferred embodiment of the present invention, the ions in the high-salinity wastewater include K+. + Na + Cl - SO4 2- And heavy metal ions.

[0019] Preferably, the heavy metal ions include As and Zn. 2+ Pb 2+ Cd 2+ and Tl + .

[0020] It is worth noting that the As ions in the heavy metal ions mainly exist as AsO4 in high-salt wastewater. 3- H2AsO3 - It exists in the form of.

[0021] As a preferred embodiment of the present invention, the precipitant in step (1) includes sodium hydroxide and / or sodium sulfide and polyacrylamide.

[0022] Preferably, the mass ratio of sodium hydroxide, sodium sulfide and polyacrylamide is 1:1:1 to 3, for example, it can be 1:1:1, 1:1:1.4, 1:1:1.8, 1:1:2.2, 1:1:2.6 or 1:1:3, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the mass ratio of the precipitant to the high-salt wastewater is 1.5 to 2.5:1000, for example, it can be 1.5:1000, 1.7:1000, 1.9:1000, 2.1:1000, 2.3:1000 or 2.5:1000, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] In this invention, the precipitant is a mixture of sodium hydroxide, sodium sulfide, and polyacrylamide. Sodium hydroxide reacts with heavy metal ions in the high-salinity wastewater to form insoluble hydroxides, thereby removing heavy metals. Simultaneously, it increases the pH of the high-salinity wastewater, promoting the precipitation of heavy metal ions. Sodium sulfide reacts with lead, zinc, and cadmium ions to form insoluble metal sulfides, effectively removing heavy metal ions from the high-salinity wastewater. Polyacrylamide, as a high-molecular-weight flocculant, has a strong coagulation effect and can promote the coagulation and sedimentation of suspended solids in the wastewater through physical or chemical adsorption. Furthermore, polyacrylamide enhances the flocculation effect of the precipitate formed by sodium hydroxide and sodium sulfide, making the precipitate easier to separate and thus enhancing the removal of heavy metal ions. In summary, the three components of the precipitant complement each other and are indispensable, ensuring both efficient precipitation reaction and excellent flocculation effect, thereby achieving highly efficient removal of heavy metal ions from high-salinity wastewater.

[0025] As a preferred technical solution of the present invention, the stirring rate of the stirring reaction in step (1) is 400 to 600 r / min, for example, it can be 400 r / min, 440 r / min, 480 r / min, 520 r / min, 560 r / min or 600 r / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the stirring reaction time in step (1) is 15 to 30 minutes, for example, it can be 15 minutes, 18 minutes, 21 minutes, 24 minutes, 27 minutes or 30 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] As a preferred technical solution of the present invention, the freezing crystallization temperature in step (2) is -5 to 0°C, for example, it can be -5°C, -4°C, -3°C, -2°C, -1°C or 0°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the freezing and crystallization time in step (2) is 0.5 to 1.5 hours, for example, 0.5 hours, 0.7 hours, 0.9 hours, 1.1 hours, 1.3 hours or 1.5 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] In this invention, sodium sulfate is first recovered through freeze crystallization. The purpose is that the solubility of sodium sulfate decreases significantly with decreasing temperature, while the solubility of other impurities changes less. Furthermore, the removal of sodium sulfate reduces its impact on the subsequent recovery processes of sodium chloride and potassium chloride. The freeze crystallization temperature is -5 to 0°C. If the freeze crystallization temperature is too high, the crystallization rate will slow down, thus affecting the crystallization efficiency and purity. Conversely, if the freeze crystallization temperature is too low, it will affect the quality of the crystals, resulting in excessively small crystals. Other impurities will also crystallize, leading to a decrease in product purity.

[0030] As a preferred technical solution of the present invention, the multi-effect evaporation in step (3) includes triple-effect evaporation.

[0031] Preferably, the temperature of the multi-effect evaporation in step (3) is 90 to 110°C, for example, it can be 90°C, 94°C, 98°C, 102°C, 106°C or 110°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the time for multi-effect evaporation in step (3) is 20 to 40 minutes, for example, 20 minutes, 24 minutes, 28 minutes, 32 minutes, 36 minutes or 40 minutes, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] In this invention, sodium chloride is recovered from wastewater through multi-effect evaporation. If the temperature is too high during the evaporation process, excessive water evaporation may occur, which may cause KCl crystallization and interfere with the NaCl recovery process. If the temperature is too low, insufficient water evaporation will occur, affecting the NaCl recovery effect. If the evaporation time is too long, energy consumption will increase. Under low temperature conditions, too much NaCl will be retained in the solution.

[0034] As a preferred technical solution of the present invention, step (4) further includes flash evaporation of the three filtrates before cooling and crystallization.

[0035] Preferably, the endpoint temperature of the flash evaporation treatment is 45-65°C, for example, it can be 45°C, 49°C, 53°C, 57°C, 61°C or 65°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] As a preferred technical solution of the present invention, the cooling crystallization temperature in step (4) is 45 to 65°C, for example, it can be 45°C, 49°C, 53°C, 57°C, 61°C or 65°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the cooling crystallization time in step (4) is 10 to 30 minutes, for example, it can be 10 minutes, 14 minutes, 18 minutes, 22 minutes, 26 minutes or 30 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] In this invention, potassium chloride is recovered from wastewater by cooling crystallization. If the cooling crystallization temperature is too high, the solubility of KCl will be high, resulting in slow crystallization and reduced recovery rate. If the temperature is too low, KCl will precipitate excessively, and impurities will also precipitate, affecting product quality and continuous production.

[0039] In this invention, the cold source used in the freezing crystallization and cooling crystallization processes includes industrial cooling water or mechanical refrigeration. This invention further reduces energy consumption through a rational cooling design. Compared to traditional high-temperature evaporation processes, the application of a low-temperature cold source significantly improves the energy-saving effect of wastewater resource utilization and reduces steam consumption (approximately 30%–50%), giving this invention a significant advantage in energy efficiency.

[0040] As a preferred embodiment of the present invention, the resource-based treatment method for high-salinity wastewater provided by the present invention includes the following steps:

[0041] (1) Mix the precipitant and high-salt wastewater at a mass ratio of 1.5 to 2.5:1000, and stir at a stirring rate of 400 to 600 r / min for 15 to 30 minutes to obtain a primary filtrate by solid-liquid separation.

[0042] The precipitant comprises sodium hydroxide, sodium sulfide, and polyacrylamide in a mass ratio of 1:1:1 to 3.

[0043] (2) The primary filtrate obtained in step (1) is subjected to freeze crystallization at -5 to 0℃ for 0.5 to 1.5 h. After solid-liquid separation, sodium sulfate and secondary filtrate are obtained.

[0044] (3) The secondary filtrate obtained in step (2) is subjected to multi-effect evaporation for 20 to 40 minutes at 90 to 110°C. After solid-liquid separation, sodium chloride and tertiary filtrate are obtained.

[0045] (4) After flash evaporation of the filtrate obtained in step (3), the solution is cooled and crystallized at 45-65°C for 10-30 minutes. After solid-liquid separation, potassium chloride and the fourth filtrate are obtained.

[0046] The four filtrates are reused for the freeze crystallization in step (2).

[0047] The apparatus system used in the above-mentioned resource-based treatment method for high-salinity wastewater includes: a heavy metal removal unit, a freeze crystallization unit, an evaporation crystallization unit, and a cooling crystallization unit, which are connected in sequence through a conveying pipeline.

[0048] Preferably, the heavy metal removal unit includes a stirred reactor and a solid-liquid separator connected in sequence.

[0049] Preferably, the inlet of the stirred reactor is equipped with a flow control device to control the flow rate of high-salt wastewater into the stirred reactor, so as to ensure the sufficiency of the stirring reaction in the high-salt wastewater.

[0050] Preferably, the freeze crystallization unit includes a cooling crystallization pool and a crystallization separation device connected in sequence.

[0051] Preferably, the cooling crystallization pool is equipped with a cooling circulation device to provide and maintain a low-temperature environment for the cooling crystallization pool.

[0052] Preferably, the cooling circulation device includes a cooling water circulation pump or a heat exchanger.

[0053] Preferably, the evaporation crystallization apparatus includes a multi-effect evaporator and a crystallization separator connected in sequence.

[0054] Preferably, the evaporation crystallization apparatus further includes a steam compressor for compressing the steam generated during the multi-effect evaporation process to improve the energy efficiency of the apparatus system.

[0055] Preferably, the cooling crystallization unit includes a cooler and a solid-liquid separation device connected in sequence.

[0056] Preferably, the liquid outlet of the solid-liquid separation device is equipped with a circulation pump to pump the filtrate from the fourth pass back into the cooling crystallization tank, forming a closed-loop circulation, thereby achieving zero wastewater discharge.

[0057] Preferably, the cooler includes a cooling water circulation device to provide the low-temperature cold source required for cooling crystallization, ensuring the stability of the cooling crystallization process.

[0058] Preferably, the device system further includes a control system for monitoring and adjusting the flow rate and pressure of the four filtrates during the reuse process in step (4) to ensure the continuous operation of the device system.

[0059] Preferably, the conveying flow rate is 12-16 m³ / s. 3 / h, for example, could be 12m 3 / h、13m 3 / h, 14m 3 / h, 15m 3 / h or 16m 3 / h, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0060] Preferably, the conveying pressure is 165-170 kPa, for example, it can be 165 kPa, 166 kPa, 167 kPa, 168 kPa, 169 kPa or 170 kPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] It is worth noting that the resource recovery method described in this invention is a continuous treatment method. By employing a continuously connected device, continuous treatment of wastewater is achieved, further improving treatment efficiency.

[0062] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] (1) The resource recovery method provided by the present invention firstly removes heavy metals in wastewater effectively through a precipitant (with a removal rate of over 95%), ensuring that the subsequent crystallization process is not contaminated; then, by combining freeze crystallization, multi-effect evaporation and cooling crystallization, the crystallization and recovery of different components in high-salt wastewater are realized, and the scaling problem is reduced.

[0065] (2) This invention combines freeze crystallization, multi-effect evaporation and cooling crystallization to achieve stepwise crystallization recovery of sodium sulfate, sodium chloride and potassium chloride by utilizing different temperature ranges. The recovery rates of sodium sulfate, sodium chloride and potassium chloride are all not less than 90%, which meets the usage standards of the chemical, agricultural and food industries and ensures that the recovered products have high industrial application value.

[0066] (3) The resource utilization method provided by the present invention reuses the filtrate from the four times for freezing and crystallization, thereby forming a closed loop in the treatment method, realizing zero discharge of wastewater and full recovery of resources, significantly improving the overall resource utilization rate, reducing environmental pollution, and meeting environmental protection requirements.

[0067] (4) The resource utilization method provided by the present invention makes reasonable use of low temperature cold source for freezing crystallization and cooling crystallization, which significantly improves the energy-saving effect and reduces the amount of steam used (30-50%) compared with the traditional high temperature evaporation process. Attached Figure Description

[0068] Figure 1 This is a flowchart of a method for resource-based treatment of high-salinity wastewater provided in Embodiment 1 of the present invention. Detailed Implementation

[0069] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0070] The ion composition and content of the high-salinity wastewater treated in the following examples and comparative examples are shown in Table 1:

[0071] Table 1

[0072] <![CDATA[K + ]]> <![CDATA[Na + ]]> <![CDATA[Cl - ]]> <![CDATA[SO4 2- ]]> <![CDATA[Pb 2+ ]]> <![CDATA[Cd 2+ ]]> <![CDATA[Tl + ]]> <![CDATA[Zn 2+ ]]> As Content (mg / L) 32440 68790 109890 32150 1.0 0.5 6.0 4.0 0.3

[0073] Example 1

[0074] This embodiment provides a resource-based treatment method for high-salinity wastewater, such as... Figure 1 As shown, the resource recovery method includes the following steps:

[0075] (1) The precipitant and high-salt wastewater were mixed at a mass ratio of 2:1000, and the mixture was stirred at a stirring rate of 500r / min for 25min before solid-liquid separation was carried out to obtain the first filtrate.

[0076] The precipitant comprises sodium hydroxide, sodium sulfide, and polyacrylamide in a mass ratio of 1:1:2;

[0077] (2) The primary filtrate obtained in step (1) was subjected to freeze crystallization at -3℃ for 1 hour. After solid-liquid separation, sodium sulfate and secondary filtrate were obtained.

[0078] (3) The secondary filtrate obtained in step (2) was subjected to triple-effect evaporation for 30 minutes at 100℃. After solid-liquid separation, sodium chloride and tertiary filtrate were obtained.

[0079] (4) After flash evaporation of the filtrate obtained in step (3), the solution is cooled and crystallized at 55°C for 20 min. After solid-liquid separation, potassium chloride and the fourth filtrate are obtained.

[0080] The four filtrates are reused for the freeze crystallization in step (2).

[0081] Example 2

[0082] This embodiment provides a method for the resource-based treatment of high-salinity wastewater, which includes the following steps:

[0083] (1) The precipitant and high-salt wastewater were mixed at a mass ratio of 1.5:1000, and the mixture was stirred at a stirring rate of 400r / min for 30min before solid-liquid separation was carried out to obtain the first filtrate.

[0084] The precipitant comprises sodium hydroxide, sodium sulfide, and polyacrylamide in a mass ratio of 1:1:1;

[0085] (2) The primary filtrate obtained in step (1) was subjected to freeze crystallization at -5℃ for 0.5h. After solid-liquid separation, sodium sulfate and secondary filtrate were obtained.

[0086] (3) The secondary filtrate obtained in step (2) was subjected to triple-effect evaporation for 40 minutes at 90℃. After solid-liquid separation, sodium chloride and tertiary filtrate were obtained.

[0087] (4) After flash evaporation of the filtrate obtained in step (3), the solution is cooled and crystallized at 45°C for 10 min. After solid-liquid separation, potassium chloride and the fourth filtrate are obtained.

[0088] The four filtrates are reused for the freeze crystallization in step (2).

[0089] Example 3

[0090] This embodiment provides a method for the resource-based treatment of high-salinity wastewater, which includes the following steps:

[0091] (1) The precipitant and high-salt wastewater were mixed at a mass ratio of 2.5:1000, and the mixture was stirred at a stirring rate of 600r / min for 15min before solid-liquid separation was carried out to obtain the first filtrate.

[0092] The precipitant comprises sodium hydroxide, sodium sulfide, and polyacrylamide in a mass ratio of 1:1:3;

[0093] (2) The primary filtrate obtained in step (1) was subjected to freeze crystallization at 0℃ for 1.5h. After solid-liquid separation, sodium sulfate and secondary filtrate were obtained.

[0094] (3) The secondary filtrate obtained in step (2) was subjected to triple-effect evaporation for 20 minutes at 110℃. After solid-liquid separation, sodium chloride and tertiary filtrate were obtained.

[0095] (4) After flash evaporation of the filtrate obtained in step (3), the solution is cooled and crystallized at 65°C for 30 minutes. After solid-liquid separation, potassium chloride and the fourth filtrate are obtained.

[0096] The four filtrates are reused for the freeze crystallization in step (2).

[0097] Example 4

[0098] This embodiment provides a resource-based treatment method for high-salinity wastewater, which differs from Embodiment 1 only in that:

[0099] In this embodiment, the temperature of the freeze-crystallization in step (2) is adjusted to -8℃.

[0100] Example 5

[0101] This embodiment provides a resource-based treatment method for high-salinity wastewater, which differs from Embodiment 1 only in that:

[0102] In this embodiment, the freezing and crystallization temperature in step (2) is adjusted to 2°C.

[0103] Example 6

[0104] This embodiment provides a resource-based treatment method for high-salinity wastewater. The only difference between this resource-based treatment method and Embodiment 1 is that:

[0105] In this embodiment, the temperature of the multi-effect evaporation in step (3) is adjusted to 80°C.

[0106] Example 7

[0107] This embodiment provides a resource-based treatment method for high-salinity wastewater. The only difference between this resource-based treatment method and Embodiment 1 is that:

[0108] In this embodiment, the temperature of the multi-effect evaporation in step (3) is adjusted to 120°C.

[0109] Example 8

[0110] This embodiment provides a resource-based treatment method for high-salinity wastewater. The only difference between this resource-based treatment method and Embodiment 1 is that:

[0111] In this embodiment, the cooling crystallization temperature in step (4) is adjusted to 40°C.

[0112] Example 9

[0113] This embodiment provides a resource-based treatment method for high-salinity wastewater. The only difference between this resource-based treatment method and Embodiment 1 is that:

[0114] In this embodiment, the cooling crystallization temperature in step (4) is adjusted to 70°C.

[0115] Example 10

[0116] This embodiment provides a resource-based treatment method for high-salinity wastewater. The only difference between this resource-based treatment method and Embodiment 1 is that:

[0117] In this embodiment, the precipitant in step (1) is adjusted to be sodium hydroxide and sodium sulfide in a mass ratio of 1:1.

[0118] Example 11

[0119] This embodiment provides a resource-based treatment method for high-salinity wastewater. The only difference between this resource-based treatment method and Embodiment 1 is that:

[0120] This embodiment omits sodium hydroxide and sodium sulfide from the precipitant in step (1).

[0121] Example 12

[0122] This embodiment provides a resource-based treatment method for high-salinity wastewater. The only difference between this resource-based treatment method and Embodiment 1 is that:

[0123] In this embodiment, the mass ratio of the precipitant and the high-salt wastewater in step (1) is adjusted to 5:1000. The precipitant includes sodium hydroxide, sodium sulfide and polyacrylamide in a ratio of 2:1:3.

[0124] Comparative Example 1

[0125] This comparative example provides a resource-based treatment method for high-salinity wastewater. The only difference between this resource-based treatment method and Example 1 is that:

[0126] This comparative example omits the process of mixing the precipitant and stirring it in step (1), that is, directly freezing and crystallizing the high-salt wastewater.

[0127] Comparative Example 2

[0128] This comparative example provides a resource-based treatment method for high-salinity wastewater. The only difference between this resource-based treatment method and Example 1 is that:

[0129] This comparative example reverses the order of the freeze crystallization and multi-effect evaporation operations. Specifically, after multi-effect evaporation of the filtrate obtained in step (1), freeze crystallization and cooling crystallization are performed.

[0130] Comparative Example 3

[0131] This comparative example provides a resource-based treatment method for high-salinity wastewater. The only difference between this resource-based treatment method and Example 1 is that:

[0132] This comparative example reverses the order of operations for multi-effect evaporation and cooling crystallization, i.e., after cooling and crystallizing the secondary filtrate obtained in step (2), multi-effect evaporation is then performed.

[0133] Comparative Example 4

[0134] This comparative example provides a resource-based treatment method for high-salinity wastewater. The only difference between this resource-based treatment method and Example 1 is that:

[0135] The comparative example adjusts the operation process as follows: the filtrate obtained in step (1) is subjected to multi-effect evaporation, cooling crystallization and freezing crystallization in sequence.

[0136] Performance testing:

[0137] The purity and yield of sodium sulfate, sodium chloride, and potassium chloride obtained in the above examples and comparative examples were tested, and the results are shown in Table 2.

[0138] Table 2

[0139]

[0140]

[0141] According to Table 1, the following points can be observed:

[0142] (1) Comprehensive analysis of Examples 1-3 shows that the resource recovery method provided by the present invention can achieve stepwise crystallization recovery of sodium sulfate, sodium chloride and potassium chloride, and the recovery rate is not less than 99%, which meets the usage standards of the chemical, agricultural and food industries and ensures that the recovered products have high industrial application value.

[0143] (2) Comprehensive analysis of Examples 1 and 4-5 shows that during the treatment of high-salt wastewater, when the temperature of the freezing crystallization is too high, the crystallization rate will be reduced, thereby increasing energy consumption; conversely, when the temperature of the freezing crystallization is too low, impurities will be precipitated, resulting in a decrease in the purity of sodium sulfate.

[0144] (3) Comprehensive analysis of Examples 1 and 6-7 shows that during the treatment of high-salt wastewater, when the temperature of the multi-effect evaporation is too high, it will lead to excessive evaporation of water and precipitation of a small amount of KCl crystals, which will affect the purity of NaCl; conversely, when the temperature of the multi-effect evaporation is too low, it will lead to insufficient evaporation of water and affect the recovery effect of NaCl.

[0145] (4) Comprehensive analysis of Examples 1 and 8-9 shows that during the treatment of high-salt wastewater, when the cooling crystallization temperature is too high, the solubility of KCl will be high, resulting in slow crystallization; conversely, when the cooling crystallization temperature is too low, KCl will precipitate excessively, and impurities will also precipitate, affecting product quality.

[0146] (5) Comprehensive analysis of Examples 1 and 10-12 shows that adjusting the composition of the precipitant during the treatment of high-salt wastewater will affect the separation effect of heavy metal ions in the wastewater.

[0147] If the use of polyacrylamide is omitted, the flocculation effect will be reduced, resulting in the incomplete removal of particulate impurities in the wastewater, which in turn reduces the purity and yield of the obtained product.

[0148] If sodium hydroxide and sodium sulfide are omitted, insoluble hydroxides or metal sulfides cannot be formed, resulting in some heavy metal ions not being completely removed, which reduces the purity of the product.

[0149] When the sodium hydroxide content in the precipitant is too high, it will cause the precipitate in the wastewater to be finer and more viscous, increasing the difficulty of separation.

[0150] (6) Comprehensive analysis of Example 1 and Comparative Example 1 shows that the mixing of precipitant and high-salt wastewater can effectively remove heavy metals from the wastewater. If this step is omitted, it will lead to the crystallization of heavy metal salts and affect product quality.

[0151] (7) Comprehensive analysis of Example 1 and Comparative Examples 2-4 shows that changing the order of freezing crystallization, multi-effect evaporation and cooling crystallization in the resource recovery process provided by the present invention will result in uneven crystallinity of each ion in the solution, thus making it impossible to effectively separate the three high-purity salt products; (1) If cooling crystallization is performed first, KCl cannot meet the crystallization conditions in the solution at 45-65℃; (2) If multi-effect evaporation is performed first, not only will NaCl precipitate, but Na2SO4 will also precipitate during evaporation, resulting in a decrease in the purity of the final product; (3) If freezing crystallization is performed first, followed by cooling crystallization to precipitate KCl, since the solution has not been concentrated, KCl cannot be precipitated in the temperature range of 45-65℃.

[0152] In summary, this invention, through sequential freezing crystallization, multi-effect evaporation, cooling crystallization, and recycling, can effectively separate and recover sodium, potassium, and other components from high-salt wastewater, producing industrially valuable sodium sulfate, sodium chloride, and potassium chloride products, reducing the salt content of wastewater, and realizing the resource utilization of wastewater.

[0153] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for the resource-based treatment of high-salinity wastewater, characterized in that, The resource recovery method includes the following steps: (1) Mix high-salt wastewater and precipitant, stir and react, then perform solid-liquid separation to obtain primary filtrate; The precipitant includes sodium hydroxide, sodium sulfide, and polyacrylamide; the mass ratio of sodium hydroxide, sodium sulfide, and polyacrylamide is 1:1:1~3; the mass ratio of the precipitant to the high-salinity wastewater is 1.5~2.5:1000; (2) The primary filtrate obtained in step (1) is subjected to freeze crystallization, and sodium sulfate and secondary filtrate are obtained after solid-liquid separation; the freeze crystallization temperature is -5~0℃; (3) The secondary filtrate obtained in step (2) is subjected to multi-effect evaporation, and sodium chloride and tertiary filtrate are obtained after solid-liquid separation; the temperature of the multi-effect evaporation is 90~110℃; (4) Cool the filtrate obtained in step (3) to crystallize it, and after solid-liquid separation, potassium chloride and filtrate are obtained; before cooling crystallization, the filtrate is further subjected to flash evaporation treatment; the final temperature of the flash evaporation treatment is 45~65℃; the temperature of cooling crystallization is 45~65℃. The four filtrates are reused for the freeze crystallization in step (2).

2. The resource-based treatment method for high-salinity wastewater according to claim 1, characterized in that, The ions in the high-salinity wastewater include K+. + Na + Cl - SO4 2- And heavy metal ions.

3. The resource-based treatment method for high-salinity wastewater according to claim 2, characterized in that, The heavy metal ions include Zn 2+ Pb 2+ Cd 2+ and Tl + .

4. The resource-based treatment method for high-salinity wastewater according to claim 2, characterized in that, The high-salt wastewater also contains As.

5. The method for resource-based treatment of high-salinity wastewater according to claim 1, characterized in that, The stirring rate of the stirring reaction in step (1) is 400~600 r / min.

6. The resource-based treatment method for high-salinity wastewater according to claim 5, characterized in that, The stirring reaction time in step (1) is 15~30 min.

7. The method for resource-based treatment of high-salinity wastewater according to claim 1, characterized in that, The freezing and crystallization time in step (2) is 0.5~1.5h.

8. The method for resource-based treatment of high-salinity wastewater according to claim 1, characterized in that, The multi-effect evaporation in step (3) includes triple-effect evaporation.

9. The method for resource-based treatment of high-salinity wastewater according to claim 1, characterized in that, The time for multi-effect evaporation in step (3) is 20~40 min.

10. The method for resource-based treatment of high-salinity wastewater according to any one of claims 1-8, characterized in that, The cooling and crystallization time in step (4) is 10~30 min.

11. The method for resource-based treatment of high-salinity wastewater according to claim 1, characterized in that, The resource recovery method includes the following steps: (1) Mix the precipitant and high-salt wastewater at a mass ratio of 1.5~2.5:1000, stir at a stirring rate of 400~600r / min for 15~30min, and then separate the solid and liquid to obtain the first filtrate. The precipitant comprises sodium hydroxide, sodium sulfide, and polyacrylamide in a mass ratio of 1:1:1~3; (2) The primary filtrate obtained in step (1) is subjected to freeze crystallization at -5~0℃ for 0.5~1.5h, and sodium sulfate and secondary filtrate are obtained after solid-liquid separation; (3) The secondary filtrate obtained in step (2) is subjected to multi-effect evaporation for 20 to 40 minutes at 90 to 110°C. After solid-liquid separation, sodium chloride and tertiary filtrate are obtained. (4) After flash evaporation of the filtrate obtained in step (3), the liquid is cooled and crystallized at 45-65℃ for 10-30 minutes. After solid-liquid separation, potassium chloride and the fourth filtrate are obtained. The four filtrates are reused for the freeze crystallization in step (2).

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